This is a Non-Federal dataset covered by different Terms of Use than

National Geochemical Survey Locations and Results for Iowa

Metadata Updated: July 19, 2013

The United States Geological Survey (USGS), in collaboration with other state and federal agencies, industry, and academia, is conducting a National Geochemical Survey (NGS) to produce a database of geochemical information for the United States based primarily on stream sediments, analyzed using a single set of methods. This data set will comprise a national-scale geochemical coverage of the US, and will enable construction of geochemical maps, refine estimates of baseline chemical element concentrations in the sampled media, and provide context for a wide variety of geological and environmental studies. The goal of the NGS is to analyze at least one stream-sediment sample within every 289 km2 area across the US, using a consistent set of analytical methods, substituting soil samples where necessary. The survey incorporates geochemical data from a variety of sources, including existing analyses in USGS databases, reanalyses of samples in USGS archives, and analyses of recently collected samples. Currently, the NGS data covers ~71% of the land area of the US, and includes samples from all 50 states. The Iowa Geological Survey (IGS) of the Iowa Department of Natural Resources (IDNR) entered into an agreement with the USGS in September of 2002 whereby the IGS would design a database for field parameters and collect two soil sample sets. One set for the USGS to process and analyze, and one set to reposit. Field parameters included ambient site conditions, GPS location, elevation, landscape position, vegetation type, NRCS soil type, sample depth, and soil horizon, texture, color and moisture. Digital photographs were taken of the site and samples at each location. The samples were sieved to -100 mesh, then analyzed for 40 elements using inductively coupled plasma-atomic emission spectrometry/acid dissolution (ICP40), and 6 elements using atomic absorption spectrometry (AA). Arsenic (As) and gold (Au) were analyzed for using both methods. Analyses were performed by the USGS or an approved laboratory, using standard methods and an U.S.E.P.A. approved quality assurance/quality control plan. To maximize statistical reliability, sample collection in Iowa was based on a 17 km x 17 km grid, displayed on USGS 1:250,000 quad maps. Each grid or cell was identified by quad name and cell column and row position, and divided into four 72 km2 quadrants, and one was selected at random for sampling. The IGS selected specific sampling sites within the selected quadrants. To separate leached horizons from those accumulating CO3, one shallow (0-8 inches) and one deep (12-24 inches) sample were collected from 463 regular and 72 analysis of variance (AOV) sites from May through August of 2003 and shipped to the USGS in August. Randomly selected AOV sites were sampled to provide a data set for statistical analysis to test the adequacy of the samples to measure differences of sediment chemistry between cells, within cells, within sites, and between chemical analyses. "AOV1" was collected within the designated quadrant of the cell, then one of the three other quadrants of the cell were selected at random for "AOV2" and "AOV3" which were collected about 10 feet apart, preferably within the same soil type. The field data were described on data collection sheets and later transferred to the IGS network through an entry routine on a daily to weekly basis. The DBASE entry routine and database were developed and maintained by IGS personnel, then after the analyses were performed, the data were joined with the soil sample analyses by USGS personnel. The joined database can be accessed at the IGS website at, and for a detailed description of the NGS, visit the USGS website at

Access & Use Information

Non-Federal: This dataset is covered by different Terms of Use than License: No license information was provided.

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Metadata Date March 4, 2008
Metadata Created Date July 19, 2013
Metadata Updated Date July 19, 2013
Reference Date(s) March 23, 2006 (publication)
Frequency Of Update asNeeded

Metadata Source

Harvested from Iowa Geospatial Data Clearinghouse

Additional Metadata

Resource Type Dataset
Metadata Date March 4, 2008
Metadata Created Date July 19, 2013
Metadata Updated Date July 19, 2013
Reference Date(s) March 23, 2006 (publication)
Responsible Party Iowa Department of Natural Resources (Point of Contact)
Contact Email
Access Constraints Use Constraints: The development of the coverages in the NRGIS Library represents a major investment of staff time and effort. As a professional responsibility, the the Iowa DNR expects to receive proper credit when these GIS coverages are utilized. The Department also expects that the original documentation will remain with any redistribution of these coverages. Mercury is a difficult element for which to obtain accurate analyses. Samples can easily be contaminated with Hg during handling, storage, and preparation for analysis. Mercury can also be lost from samples during the drying process or while in storage. Recently collected samples were handled and stored in a manner that should result in few such problems. However, many Hg data in the NGS are based on reanalyses of archival samples, e.g., NURE samples, that were neither collected using protocols appropriate for Hg analysis, nor stored under conditions that would necessarily preserve the original Hg concentrations. Some NURE samples in the eastern US were very likely contaminated by Hg at some point after collection (e.g., all samples from Allegany County, Maryland). At the present time, it is not known which archival samples may have been contaminated with Hg in the laboratory, and thus extreme caution should be exercised in interpreting NGS data., Access Constraints: None
Bbox East Long -90.230266
Bbox North Lat 43.459707
Bbox South Lat 40.527909
Bbox West Long -96.428030
Coupled Resource
Frequency Of Update asNeeded
Harvest Object Id 69858702-5cb5-4dd7-8252-5cafe2224113
Harvest Source Id 2abfde33-b6a6-461c-879b-612565f3a067
Harvest Source Title Iowa Geospatial Data Clearinghouse
Licence Although efforts have been made in correcting errors in order to make this information useful to the Department, the Department assumes no responsibility for errors in the information. Similarly, the Department assumes no responsibility for the consequences of inappropriate uses or interpretations of the data made by anyone to whom this data has been made available. The Department bears no responsibility to inform users of any changes made to this data. Anyone using this data is advised that precision implied by the coverage may far exceed actual precision. Comments on this data are invited and the Department would appreciate that documented errors be brought to staff attention.
Metadata Language
Metadata Type geospatial
Spatial Data Service Type
Spatial Reference System
Spatial Harvester True

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